Dark Green Brown vs Armor Green

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Armor Green is more muted, cooler than Dark Green Brown.

Can I use Armor Green instead of Dark Green Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Armor Green is more muted, cooler than Dark Green Brown.

Can I use Dark Green Brown instead of Armor Green?

The same difference applies the other way round: Dark Green Brown is more saturated, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.